1. Field of Invention
This invention relates to novel composite pigments, their preparation and their use such, for example, in inks, varnishes, plastic materials.
2. Prior Art
Prior to the present invention there has been extensive work in the preparation of pigments containing inorganic and organic portions to impart certain desirable properties to the pigment. For example, the prior art has sought to obtain pigments showing dulling properties comparable with those of traditional inorganic pigments, such as for instance chrome yellows, and molybedenum oranges, whose preparation and use meet with ever increasing limitations because of their toxicity.
There has been suggested a number of pigments based on the attribution and/or boosting of the pigmentary properties in organic dyes of the acid type, by means of varnishing and supporting technologies which may lead to complexes of a pigmentary character, and consisting of an organic portion and an inorganic portion.
In this connection, it is known that the acid dyes are compounds which contain in their molecule acid groups (COOH, SO.sub.3 H), which confer to the products a solubility in water or in alkaline media, and are mainly used in the dyeing of natural or synthetic polyamidic fibres.
It is equally known that some of these dyes may form insoluble compounds ("toners"), lacquers, with alkaline earthy metal salts (Ca, Ba, Mg, Sr) and/or of another nature (Mn, Zn, Al). Such compositions, however, do not possess the hiding power of the traditional inorganic pigments (chromium yellows, molybedenum oranges). On the contrary, in the stage of dyeing the manufactured articles, they are mechanically mixed together with inorganic fillers or charges of various kinds. Depending on the type of application, the fillers or charges may consist of compounds of either modest (for instance barytes) or of high hiding power (e.g. TiO.sub.2).
Nonetheless, in the case of the use of fillers of a high hiding power (TiO.sub.2), there will be required the use of compounds highly coloured and/or in the great quantity in order to attain high colour intensities, with the consequential economical burdens.
The prior art reports also the association of the organic pigment with inorganic fillers, carried out in the stage of the synthesis of the pigment itself. In fact, there are known products of the lacquer-type, prepared in the presence of inorganic substrates, of which the most common are basic Al-compounds (basic sulphate-Pigment White 24) or mixes of BaSO.sub.4 and Al-hydrage (Pigment White 23).
According to such a technique, the precipitation of the lacquers normally occurs in two steps or stages; for instance, at first the basic aluminum sulphate is precipitated from Al-sulphate under controlled pH and temperature conditions. Thereupon, to this precipitate there are added, in the given order, the dye solution and the solution containing a metered quantity of BaCl.sub.2 so that the precipitation of the insoluble salt of the organic dye and of the Barium sulphate on the Al(OH).sub.3 substrate will occur simultaneously.
This technique will practically allow the preparation "in situ" of the inorganic substrate and the obtainment of a colour-accepting surface, but will, however, show poor hiding properties.
According to other processes, in the synthesis stage there are used inorganic substrates of high hiding properties such as e.g. TiO.sub.2). In fact, it is known that acid dyes may be made to precipitate under controlled pH-conditions (pH=2-5), in the presence of TiO.sub.2 or other inorganic substrates.
In the described cases, however, the resulting products do not offer, under the applicational profile, any appreciable advantages with respect to the mechanical mixes of single components.
According to another described method, the acid dye is made to precipitate in the form of an Al-, Cr- etc., lacquer, in the presence of lignin sulphonates.